A lithography process using near ultraviolet rays such as an I-ray as radiation has generally been used in the manufacture of integrated circuit devices. Microfabrication in a sub-quarter micron order is said to be achieved with extreme difficulty if the near ultraviolet rays are used. Therefore, achieving a higher degree of integration by using near ultraviolet rays has been difficult. For this reason, a lithography process which can achieve microfabrication with a higher degree (microfabrication of 0.20 μm or less) has been demanded.
As a means for achieving such microfabrication in the order of 0.20 μm or less, a lithography process utilizing a radiation with a wavelength shorter than that of the near ultraviolet rays is studied. As examples of radiation having such a short wavelength, deep ultraviolet rays represented by a bright line spectrum of a mercury lamp and an excimer laser, X-rays, and electron beams can be given. Among these, a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), an F2 excimer laser (wavelength: 157 nm), EUV (wavelength: 13 nm, etc.), and electron beams are attracting attention.
Along with the reduction of the radiation wavelength used in the lithography processes, a number of radiation-sensitive resin compositions suitable for use with short wavelength radiation have been proposed. As such a radiation-sensitive resin composition, a composition utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a radiation sensitive acid generator which generates an acid upon exposure to radiation (hereinafter referred to as “exposure”) have been proposed. Such a composition is hereinafter referred to as a chemically-amplified radiation sensitive composition.
As a specific example of the chemically-amplified radiation sensitive composition, a composition containing a polymer having a t-butyl ester group of a carboxylic acid or a t-butyl carbonate group of phenol and a radiation sensitive acid generator has been proposed (see Patent Document 1). This composition forms an acidic group consisting of a carboxyl group or a phenolic hydroxyl group by dissociating the t-butyl ester group or the t-butyl carbonate group in the polymer by the action of an acid which is produced by exposure to radiation. Therefore, the portion exposed to radiation (exposed area) on the resist film formed from the composition becomes easily soluble in an alkaline developer. For that reason, a desired resist pattern can be formed on a resist film by developing using an alkaline developer.
The radiation sensitive acid generator contained in the chemically-amplified radiation sensitive composition is required to have excellent transparency to radiation and to exhibit a high quantum yield when generating an acid. The acid generated by the radiation sensitive acid generator must be sufficiently strong, must have a sufficiently high boiling point, and must have an appropriate diffusion length (hereinafter referred to from time to time as “diffusion length”) in a resist film.
In order to have strong acidity and a high boiling point, and to exhibit an appropriate diffusion length, the structure of the anion moiety of an ionic radiation sensitive acid generator is important. In the case of the nonionic radiation sensitive acid generator having a sulfonyl structure or a sulfonate structure, the structure of the sulfonyl moiety is important.
For example, in the case of a radiation sensitive acid generator having a trifluoromethanesulfonyl structure, the generated acid has sufficiently high acidity and can produce a composition having sufficiently high resolution performance as a photoresist. However, such a composition has a drawback of high mask dependency as a photoresist due to the low boiling point and high diffusion length of the acid which is undesirable as a resist. For example, in the case of a radiation sensitive acid generator having a sulfonyl structure containing a large organic group such as a 10-camphor sulfonyl structure, the mask dependency is small due to the sufficiently high boiling point and sufficiently short diffusion length of the acid produced which is desirable as a resist. However, the composition exhibits only insufficient resolution performance as a photoresist due to insufficient acidity.
A radiation sensitive acid generator having a perfluoroalkylsulfonyl structure such as perfluoro-n-octanesulfonate (PFOS) has attracted an attention in recent years due to the capability of generating an acid having sufficiently high acidity, sufficiently high boiling point, and an almost appropriate diffusion length.
However, the radiation sensitive acid generators having a perfluoroalkylsulfonyl structure such as PFOS are said to cause environmental problems due to low combustibility. In addition, these compounds are suspected to accumulate in the human body. According to a report issued by the United States Environmental Protection Agency, a regulation to rule out the use of these compounds has been proposed (see Non-patent Document 1).
When more accurate control of a line width is necessary, such as a case in which the designed dimension of a device is sub-half-micron or less, a chemically-amplified resist is required to have not only excellent resolution performance, but also excellent film surface smoothness after resist pattern formation. A chemically-amplified resist having poor film surface smoothness transfers irregularities of the film surface (hereinafter referred to from time to time as “nano-edge roughness”) onto the substrate when transferring the resist pattern by etching or the like. As a result, such a chemically-amplified resist impairs the pattern dimensional accuracy. Such a chemically-amplified resist is thus reported to impair electrical properties of ultimately produced devices (see, for example, Non-patent Documents 2 to 5).    Patent Document 1: JP-B-2-27660    Non-patent Document 1: Perfluorooctyl Sulfonates; Proposed Significant New Use Rule    Non-patent Document 2: J. Photopolym. Sci. Tech., p. 571 (1998)    Non-patent Document 3: Proc. SPIE, Vol. 3333, p. 313    Non-patent Document 4: Proc. SPIE, Vol. 3333, p. 634    Non-patent Document 5: J. Vac. Sci. Technol. B16 (1), p. 69 (1998)